1. Field of the Invention
The present invention relates to a zoom lens system and an electronic image pickup apparatus using the same, and particularly to an electronic image pickup apparatus such as a video camera and a digital camera.
2. Description of the Related Art
In recent years, replacing a silver-salt film camera, a digital camera in which an object is photographed by using an electronic image pickup element such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) has become a mainstream. Furthermore, there are several categories of digital cameras in a wide range, from high-function type for professional use to a compact popular type.
A user of the popular type digital camera seeks to enjoy photography anywhere at any time with a wide range of scenes. In light of this, a small size camera, particularly a slim digital camera which can be accommodated easily in a pocket of clothes or a bag, and carried conveniently has been preferred. On the other hand, while a magnification ratio of about 3 for a digital camera of a compact type has been common, a camera of a higher magnification ratio than the conventional one for widening a photography area has been sought.
On the other hand, since a thickness of a camera is determined by a size of a lens barrel, for achieving a slimming of the camera, slimming of the lens barrel is effective.
Recently, a so-called collapsible barrel in which, when the camera is in use, the lens barrel is pushed out from a camera body, and is used while carrying the camera while not in use has been generally used. Therefore, taking into consideration the slimming of the lens barrel when collapsed, a zoom lens has been sought.
A compact zoom lens system in which a comparatively high magnification ratio is secured by forming a type, including in order from an object side, a first lens unit having a positive refracting power, a second lens unit having a negative refracting power, a third lens unit having a positive refracting power, and a fourth lens unit having a positive refractive power, and the first lens unit is formed by one or two lenses has been known in Japanese Patent Laid-open Publication No. 2003-315676.
In the zoom lens system disclosed in Japanese Patent Application Laid-open Publication No. 2003-315676, an idea has been devised to decrease a thickness of the first lens unit by decreasing the number of lenses in the first lens unit. Particularly, since a height from an optical axis of off-axis rays is increased in the first lens unit, when an attempt is made to secure a necessary amount of an edge thickness of a lens, an axial edge thickness tends to increase remarkably. Furthermore, when the number of lenses in the first lens unit increases, since a position of entrance pupil incidence becomes distant as viewed from the object side, the height of the off-axis rays passing through the first lens unit increases more and more, and the longitudinal thickness for securing the edge thickness is required to be even more. As a matter of course, the longitudinal thickness is increased in accordance with an increase in the number of lenses.
Consequently, with the increase in the number of lenses, a size in a radial direction and the longitudinal thickness of this unit is increased to be more than required, and even in the collapsed state, the lens barrel cannot be made sufficiently compact. From this viewpoint, letting the structure such that the first lens unit is made of a large number of lenses is preferable for an object of making the (lens) barrel compact.